1. Field of the Invention
The invention relates in general to overdriving circuits of color sequential displays, and more particularly to line compensated overdriving circuits of color sequential liquid crystal displays (LCDs).
2. Description of the Related Art
In recent years, the flat panel display (FPD) industry has been focused on developing liquid crystal displays (LCDs), especially on developing thin film transistor (TFT) LCDs, and hoping to replace the role of cathode ray tube (CRT) displays in video applications. Each pixel on a TFT LCD is provided with a switching transistor for enabling image data to be written into a panel of the display.
One way of displaying the TFT LCD is to use color sequential technology. A typical frame for displaying a color image is divided into three subframes for the three primary colors of red, green and blue, and each subframe is further divided into a subframe writing period and a subframe illumination period. To display the color image, the TFT LCD is first addressed line by line by display drivers to write image data of the corresponding primary color into the pixels during the subframe writing period, in the meanwhile, capacitors located at each pixel are charged to set the liquid crystals in the pixels to their light transmittive states for displaying appropriate gray values of the corresponding primary color. Then, during the subframe illumination period, light sources, such as light emitting diode (LEDs), are turned on to display the corresponding primary color component of the color image, such that these three primary color components can be compositely perceived as a full-color image. However, the color sequential display is likely to suffer spatial intensity variations, which may cause the bottom portion of the TFT LCD to appear dimmer.
The spatial intensity variations associated with the conventional line addressing method is primarily due to insufficient pixel response times. Conventionally, during the subframe writing periods, the addressing of scan lines usually follows a unidirectional sequence such as from top to bottom or from bottom to top. FIG. 1 illustrates the pixel response time associated with a conventional line addressing method during a subframe writing period of a subframe. Taking a red subframe writing period Tr′ for illustration, as shown in FIG. 1, suppose the line addressing sequence is from top to bottom, that is, the top line of the panel is addressed first, and the bottom line of the panel is addressed last. Since the pixels on the top line are first addressed, the pixels on the top line would have sufficient time to respond, that is, have a longest pixel response time of TR1 that is substantially close to the red subframe writing period Tr′. In turn, the pixels on the next line would have a pixel response time of TR2 that is a little shorter that TR1. Yet, the pixels on the following lines would have even shorter pixel response times than TR2. Since the pixels on the bottom line are addressed last and a substantial part of the red subframe writing period has elapsed; the pixels on the bottom line would have a shortest pixel response time of TRn. The response time TRn is significantly less than TR1. Therefore, the pixels on the bottom lines, in case the line addressing sequence is from top to bottom, often do not have sufficient response times to appropriately charge the capacitors that are positioned at each pixel to set liquid crystals in the pixels to their light transmittive states for displaying the appropriate gray value. Consequently, the bottom portion of the panel in the conventional color sequential display often appears dimmer.
Hence, there is a need to provide a novel line compensated overdriving circuit and line compensated overdriving method, such that the spatial intensity variations associated with color sequential display can be greatly eliminated.